This invention relates, in general, to absorbing a shock between two tubular members and, in particular, to an apparatus for absorbing a shock between two tubular members using a plurality of layers of energy absorbing members that are sequentially deformed.
Without limiting the scope of the present invention, its background will be described with reference to perforating a subterranean formation using shaped charge perforating guns, as an example.
After drilling the section of a subterranean wellbore that traverses a formation, individual lengths of relatively large diameter metal tubulars are typically secured together to form a casing string that is positioned within the wellbore. This casing string increases the integrity of the wellbore and provides a path for producing fluids from the producing intervals to the surface. Conventionally, the casing string is cemented within the wellbore. To produce fluids into the casing string, hydraulic opening or perforation must be made through the casing string, the cement and a short distance into the formation.
Typically, these perforations are created by detonating a series of shaped charges located within the casing string that are positioned adjacent to the formation. Specifically, numerous charge carriers are loaded with shaped charges that are connected with a detonating device, such as detonating cord. The charge carriers are then connected within a tool string that is lowered into the cased wellbore at the end of a tubing string, wireline, slick line, coil tubing or the like. Once the charge carriers are properly positioned in the wellbore such that the shaped charges are adjacent to the formation to be perforated, the shaped charges are detonated. Upon detonation, each shaped charge creates a jet that blasts through a scallop or recess in the carrier, creates a hydraulic opening through the casing and cement and then penetrates the formation forming a perforation therein.
It has been found, however, that a shock wave may be generated that travels upwardly through the tools of the tool string when the shaped charge perforating guns are fired. This shock wave may damage certain tools in the tool string. In addition, it has been found that the firing bar used to contact the firing head of the perforating guns may be forced back uphole after the shaped charge perforating guns are fired. The firing bar may then damage equipment in the wellhead. Further, it has been found that once the perforating process is complete and the shaped charge perforating guns are released, they may damage the temporary plug that is commonly located within the casing below the formation that was perforated.
A need has therefore arisen for an apparatus that can be installed within the tool string that can absorb the shock wave generated by firing the shaped charge perforating guns. A need has also arisen for such an apparatus that can absorb the shock of the firing bar contacting wellhead equipment if the firing bar is forced back uphole after the shaped charge perforating guns are fired. Further, a need has arisen for such an apparatus that can absorb the shock of the shaped charge perforating guns contacting the temporary plug after the shaped charge perforating guns are released.
The present invention disclosed herein comprises a shock absorber that can be installed within a tool string to prevent damage to other downhole equipment caused by shocks. For example, the shock absorber of the present invention may be installed within the tool string to absorb the shock wave generated by firing shaped charge perforating guns. Likewise, the shock absorber of the present invention may be installed within the tool string to absorb the shock of the shaped charge perforating guns contacting the temporary plug after the shaped charge perforating guns are released. The shock absorber of the present invention may also be installed at the wellhead to absorb the shock of the firing bar if it is forced back uphole after the shaped charge perforating guns are fired. Additionally, the shock absorber of the present invention, may be used between virtually any downhole tools or between any two devices that may encounter significant one time shocks.
The shock absorber of the present invention comprises first and second tubular members that are slidably positioned relative to one another. A plurality of layers of energy absorbing members extends radially from the second tubular member such that movement of the second tubular member in a first direction relative to the first tubular member sequentially deforms the layers of energy absorbing members, thereby absorbing the shock.
In one embodiment of the shock absorber of the present invention, the second tubular member is positioned interiorly of the first tubular member. In another embodiment, the second tubular member is positioned exteriorly of the first tubular member. In one embodiment of the shock absorber of the present invention, the energy absorbing members are positioned between the first and second tubular members. The energy absorbing members may extend radially outwardly from the second tubular member or may extend radially inwardly from the second tubular member.
In one embodiment of the shock absorber of the present invention, each layer of energy absorbing members includes a plurality of shear pins. In another embodiment, each layer of energy absorbing members is a shear ring. In either embodiment, a subsequent layer of energy absorbing members may begin to deform before a previous layer of energy absorbing members is completely deformed when the second tubular member moves in the first direction relative to the first tubular member to allow for a smooth shock absorption.
In one embodiment of the shock absorber of the present invention, when the second tubular member moves in either longitudinal direction relative to the first tubular member, the energy absorbing members in adjacent layers are sequentially deformed. In this embodiment, first and second pluralities of layers of energy absorbing members extend radially from the second tubular member such that movement of the second tubular member in a first direction relative to the first tubular member sequentially deforms the layers of energy absorbing members of the first plurality of layers of energy absorbing members. Likewise, movement of the second tubular member in a second direction relative to the first tubular member sequentially deforms the layers of energy absorbing members of the second plurality of layers of energy absorbing members, thereby absorbing a shock in either direction.
The method of the present invention involves slidably positioning a first tubular member relative to a second tubular member, radially extending a plurality of layers of energy absorbing members from the second tubular member and sequentially deforming the layers of energy absorbing members as the second tubular member is moved in a first direction relative to the first tubular member, thereby absorbing the shock.